1. Field of the Invention
This invention relates to generating images, and more particularly to a light-transmission screen for projecting images in televisions, computers, and/or other display devices. The invention also relates to a method for making a light-transmission screen of the aforementioned type.
2. Description of the Related Art
Light-projection systems are used to generate images in computer monitors, televisions, and other forms of display devices. Two types of light-projection systems are available in the market today: rear-projection systems and front-projection systems. In a rear-projection system, a beam of light is projected onto the rear side of an angle-transforming screen. The screen transmits an image corresponding to the beam to a front side of the screen, where it can be seen by a viewer. Conversely, in a front-projection system a light beam is directed onto the front side of a screen where it is then reflected towards a viewer. Because of their optical properties, screens in rear-projection systems are often referred to as transmission-type screens.
Screens in conventional rear-projection displays perform a number of functions. First, these screens distribute light from an image engine into a viewing space. An example of such a viewing space is shown in FIGS. 1(a) and 1(b). In these figures, angles xcfx86V and xcfx86H define the range of viewing angles measured in vertical and horizontal directions relative to a normal (dotted line) of the screen. The viewing angles are delimited by beams 1 and 2, which correspond to places where the intensity of the projected image falls to half the value it has in the normal direction. In conventional screens, angles xcfx86V and xcfx86H are small values, typically 15xc2x0 and 35xc2x0 respectively. As a result, the images generated by these screens is projected into a small viewing area.
Second, rear-projection screens must generate images have a certain minimum resolution.
Third, rear-projection screens must provide the viewer with a high contrast image.
Fourth, rear-projection screens must provide sufficient gain to enable comfortable viewing in normal ambient light conditions.
Fifth, rear-projection screens must minimize artifacts, such as aliasing, which tends to degrade image quality. The exact parameters and specifications for each of these requirements will vary with each application.
FIG. 2a shows one type of conventional rear-projection screen which performs the aforementioned functions. These screens are formed from an array of lenticular lenses 3 separated by stripes 4 of black material. Current lenticular lens arrays generate insufficient resolution and contrast for purposes of displaying high-quality digital images.
FIG. 2b shows another type of conventional rear-projection screen. This screen includes a plurality of glass beads 5 embedded in a black matrix 6. Screens of this type are often niche-type devices and have proven unsuitable for many reasons. This is mainly attributable to their use of beads as optical elements for projecting light. For example, it is difficult to produce different angular light-distribution patterns in both vertical and horizontal directions using beads because they all have the same spherical shape and curvature. As a result, light is directed to unwanted areas, for example, towards the ceiling where there are no viewers. In addition, manufacture difficulties associated with this type of screen result in inhomogeneous placement of the beads, including areas with no beads (xe2x80x9cdrop outsxe2x80x9d).
In view of the foregoing considerations, it is clear that there is a need for a light-transmission screen which overcomes the drawbacks of conventional screens, and more specifically one which generates images of improved quality using a light-diffusing element which enhances control of the projected light at less cost and with substantially fewer manufacturing steps compared with conventional screens.
An object of the present invention is to provide a light-transmission screen which overcomes the drawbacks of conventional screens.
Another object of the present invention is to provide a light-transmission screen which generates images of improved quality compared with those produced by conventional screens.
Another object of the present invention is to provide a light-transmission screen which improves image quality by providing independent control of viewing angles in vertical and horizontal directions.
Another object of the present invention is to provide a light-transmission screen which improves image quality by achieving higher resolution than is attainable by conventional screens.
Another object of the present invention is to provide a light-transmission screen which improves image quality by achieving higher gain than is attainable by conventional screens.
Another object of the present invention is to provide a light-transmission screen which improves image quality by more effectively eliminating aliasing and other image artifacts compared with conventional screens.
Another object of the present invention is to achieve one or more of the aforementioned object using a diffusing element which projects light into a viewing area with greater control than conventional screens.
Another object of the present invention is to achieve this greater control using a diffusing element which includes a micro-lens array, where structural features of individual lenses in the array are varied so that some lenses project light in different directions and/or with different optical properties than others.
Another object of the present invention is to provide a method of making a light-transmission screen which satisfies one or more of the aforementioned objects.
Another object of the present invention is to provide a method for making a light-transmission screen which has substantially fewer manufacturing steps and is more economical to implement compared with conventional screens.
The foregoing and other objects and advantages of the present invention are achieved by providing a light-transmission screen, including a lens array comprising a plurality of lenses for projecting light, wherein at least two lenses are assigned to each pixel of the screen so as to obtain a desired screen resolution.
In accordance with another embodiment, the present invention provides a light-transmission screen, including a lens array comprising a plurality of lenses for projecting light, a mask layer, comprising a plurality of apertures, optically coupled to the lens array and positioned on a viewing side of the lens array, wherein each aperture is registered to a corresponding lens in the lens array and is adapted to pass light from its corresponding lens, wherein each pixel of the screen is generated by light from at least two lens/aperture combinations.
The present invention is also a method for making a light-transmission screen having any one or more of the aforementioned features. In accordance with one embodiment, the method includes providing a transparent substrate, coating a surface of the substrate with a mask layer, forming a micro-lens array over the mask, and forming apertures in the mask, each of which are aligned to receive light from one or more lenses in the array. The micro-lens array is preferably formed based on a stamping operation using a master. An optional step includes forming an anti-reflective coating on an opposing surface of the substrate.
In accordance with another embodiment, the present invention provides a method for making a light-transmission apparatus, which is similar to the above method except that the mask layer and lens array are formed on different sides of the substrate.
In accordance with another embodiment, the present invention provides a method for making a light-transmission apparatus which includes forming a micro-lens array on a transparent substrate, coating a surface of the substrate opposing the lens array with an adhesive, curing the adhesive, for example with UV light, and then forming a mask layer over the adhesive. The portions of the adhesive struck by UV light are removed but those portions not exposed to the light remain. As a result, the mask layer forms only over the unexposed portions of the adhesive layer leaving apertures.